Background: Group B Streptococcus (GBS) is the most common cause of invasive neonatal infection but can also cause disease in adults.
Aims: To understand the local molecular epidemiology of invasive GBS isolates, evaluate their virulome and antimicrobial resistance (AMR) patterns.
Methods: 98 invasive GBS isolates (blood, CSF and fluid) from 20 paediatric and 78 adult patients were sequenced using the Illumina Miseq platform. Analyses included MLST, AMR genes, in-silico capsular serotyping, and virulome.
Results: We identified 8 serotypes Ia, Ib, II, III, IV, V, VI and VIII. The most common MLSTs were ST1 (35%), ST17 (11%), and ST23 (11%). Previously reported hyper-virulent, III-ST17 was most pervasive in neonatal isolates (47.3%), followed by II-ST12 (10.5%) and Ib-ST8 (10.5%). In our adult cohort (> 80 years old), ST1 (V and VI) predominated (53.6%).
Regarding AMR, 82% of our isolates harboured tetracycline resistance genes, predominantly tetM (80%) and tetO (20%). Conversely, only 39% of isolates carried one or more macrolide resistance genes: ermA (45%), ermB (50%), ermT (8%) and mel (15%).
At present, we have analysed virulome data for the pilus islands (PIs). Predominant serotype III-ST17 in neonates displayed two patterns of PI expression. One group had PI-1 and PI-2b (64%), and the other only carried PI-2b (36%). In contrast, V-ST1 and VI-ST1, seen in the elderly cohort, possessed a combination of PI-1 and PI-2a (99%).
Conclusion: The relative distribution of serotypes and virulence factors differed significantly between extremes of age, favouring expansion of specific clones and acquisition of AMR and virulence genes.